1. Field of the Invention
This invention relates to electrochemical devices for generating electricity, in particular, solid oxide fuel cells and high temperature batteries. This invention also relates to solid oxide fuel cells and high temperature batteries utilizing solid carbon directly as a fuel. This invention relates to coal fueled solid oxide fuel cells. This invention also relates to sulfur-tolerant solid oxide fuel cells.
2. Description of Related Art
Fossil fuels including coal, oil and natural gas represent the majority of the world's energy supply, a fact which is likely to be true for the foreseeable future. Notwithstanding, extending the availability of these resources as well as reducing the costs and pollution associated with the use of these resources remain highly desirable objectives, objectives which can be addressed by improvements in the efficiencies of fuel utilization and fuel conversion. Methods and devices for using coal directly to produce electricity have been under investigation for the last 40 years. One prospect for improving fuel conversion efficiency is the direct conversion of carbon fuels in batteries and fuel cells. See Cherepy, N. J. et al., “Direct Conversion of Carbon Fuels in a Molten Carbonate Fuel Cell,” Journal of the Electrochemical Society, 152 (1) A80-A87 (2005). The main idea is that coal is converted to an electrically conductive form and used in a molten carbonate fuel cell. In this application, the carbon reacts with carbonate ions at the fuel cell anode and oxygen reacts with carbon dioxide at the fuel cell cathode, which reactions are carried out at a temperature of about 800° C. in accordance with the following reactions:                Anode half reaction: C+CO32−→3CO2+4e−        Cathode half reaction: O2+2CO2+4e−→2CO32−        Overall cell reaction: C+O2→CO2         
However, substantial barriers for achieving a practical carbon/air fuel cell have been encountered. These include blocking of the molten carbonate electrolyte by the build-up of ash, sluggishness of the anode reaction rate, and the high cost of carbon electrode manufacture and the complexity of distribution to the cells. An additional drawback to this fuel cell is that the cathode reaction requires at least double the amount of CO2 than oxygen, which is not possible using normal air as the oxygen source.